Abstract: The carburizing treatment of gear tooth surface can significantly increase the strength of the teeth, and then improve the load bearing and the service life of the gear. By analyzing the material characteristics of 15Cr14Co12Mo5Ni carburizing gear steel, the low pressure vacuum oil quenching equipment was used for its carburizing heat treatment. The carburizing process and parameters, quenching process and parameters were systematically investigated. The depth,microhardness, mechanical properties and microstructure of the carburizing layer after carburizing heat treatment were comprehensively measured and analyzed. Through parameters optimization, the problems of carburized blackening and hardness soft spot belt, quenching cracking, coarse structure and residual austenite were resolved. The results show that using the low pressure vacuum carburizing oil quenching equipment, increasing the ethyne flow rate of carburizing process can solve the carbon blackening problem, and the quenching cracking can be effectively controlled by room temperature oil quenching and step temperature rising for preheating, and the coarse carbide can be eliminated by increasing the carburizing temperature, shortening the carburizing time, increasing the carburizing pulse step and diffusion time. By reducing the quenching temperature for re-quenching, the transition from residual austenite to martensite can be promoted, and the "soft spot belt" between the carburizing layer and the core structure can be solved.